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Check ECC-CDH is compliant with SP800-56A-r3

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Added comments and cleared an intermediate result.
KAT tests already exist in evppkey.txt (Search for "KAS_ECC_CDH_PrimitiveTest")

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10838)
This commit is contained in:
Shane Lontis 2020-01-23 20:17:05 +10:00
parent 2eb875c925
commit f100483013
1 changed files with 21 additions and 1 deletions
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22
crypto/ec/ecdh_ossl.c
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@ -31,9 +31,14 @@ int ossl_ecdh_compute_key(unsigned char **psec, size_t *pseclen,
}
/*-
* This implementation is based on the following primitives in the IEEE 1363 standard:
* This implementation is based on the following primitives in the
* IEEE 1363 standard:
* - ECKAS-DH1
* - ECSVDP-DH
*
* It also conforms to SP800-56A r3
* See Section 5.7.1.2 "Elliptic Curve Cryptography Cofactor Diffie-Hellman
* (ECC CDH) Primitive:". The steps listed below refer to SP800-56A.
*/
int ecdh_simple_compute_key(unsigned char **pout, size_t *poutlen,
const EC_POINT *pub_key, const EC_KEY *ecdh)
@ -64,6 +69,10 @@ int ecdh_simple_compute_key(unsigned char **pout, size_t *poutlen,
group = EC_KEY_get0_group(ecdh);
/*
* Step(1) - Compute the point tmp = cofactor * owners_private_key
* * peer_public_key.
*/
if (EC_KEY_get_flags(ecdh) & EC_FLAG_COFACTOR_ECDH) {
if (!EC_GROUP_get_cofactor(group, x, NULL) ||
!BN_mul(x, x, priv_key, ctx)) {
@ -83,11 +92,20 @@ int ecdh_simple_compute_key(unsigned char **pout, size_t *poutlen,
goto err;
}
/*
* Step(2) : If point tmp is at infinity then clear intermediate values and
* exit. Note: getting affine coordinates returns 0 if point is at infinity.
* Step(3a) : Get x-coordinate of point x = tmp.x
*/
if (!EC_POINT_get_affine_coordinates(group, tmp, x, NULL, ctx)) {
ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_POINT_ARITHMETIC_FAILURE);
goto err;
}
/*
* Step(3b) : convert x to a byte string, using the field-element-to-byte
* string conversion routine defined in Appendix C.2
*/
buflen = (EC_GROUP_get_degree(group) + 7) / 8;
len = BN_num_bytes(x);
if (len > buflen) {
@ -112,6 +130,8 @@ int ecdh_simple_compute_key(unsigned char **pout, size_t *poutlen,
ret = 1;
err:
/* Step(4) : Destroy all intermediate calculations */
BN_clear(x);
EC_POINT_clear_free(tmp);
BN_CTX_end(ctx);
BN_CTX_free(ctx);